Patent Document 1 has disclosed a gas field ionization ion source (Gas Field Ion Source, abbreviated name: GFIS) having high luminance, which is provided with a micro-protrusion on an apex of an emitter electrode. Also disclosed is a focused ion beam (abbreviated name: FIB) apparatus in which this is installed so as to form a beam of gas ions of hydrogen (H2), helium (He), neon (Ne) and the like.
Different from a gallium (Ga: metal) focused ion beam apparatus (abbreviated name: Ga-FIB) derived from a liquid metal ion source (abbreviated name: LMIS) that has been often used currently, this gas focused ion beam apparatus (abbreviated name: gas FIB) has an advantage that no Ga contamination is caused onto a sample. In addition, since the GFIS has a narrow energy width of gas ions extracted therefrom and since the size of the ion generation source is small, a finer beam can be formed in comparison with that of the Ga-FIB.
This gas FIB apparatus is used as a scanning ion microscope having high resolution. In other words, the apparatus forms an image of a sample by detecting secondary particles that are emitted from the sample in synchronism with a scanning process of ions on the sample.
Patent Document 2 has disclosed a method for adjusting an extraction voltage and a gas pressure upon forming an apex structure of an emitter electrode in the GFIS.
Patent Document 3 has disclosed a method in which a supply gas and an extraction voltage are switched so as to switch the kinds of emission ions in the GFIS.